The principle of display of numbers by means of selectively illuminating a group of segments in a seven-segment-arrangement for each number is known for a long time. For example, each segment, frequently designated as a "bar", may be implemented by an electric lamp havng an elongated filament, power supply being selectively fed thereto.
Sometimes it is desired to control the segments not electrically but mechanically-optically, for example, by means of diaphragms which selectively enable or disable the light input into the segments. In such cases fiber optic light guides may be used, at one end of the guides for example, providing a small circular light input while at the other end the light guide is shaped in the desired bar form; thanks to the flexibility of the fiber optic light guides it is possible to dispose the diaphragm control for all seven segments in one straight line juxtaposed to each other. For a digitally displaying watch this is illustrated in West German Auslegeschrift (published specification) 19 19 798, FIG. 14 thereof.
Fiber optic light guides, however, are relatively expensive in particular for the display of numbers which are to be visualized over a greater distance and, thus, must have a correspondingly great size, and in particular the assembly of the flexible light guides results in complex manufacturing problems.